Cooling unit



Patented June l, 1954 COOLING UNIT Anthony G. Nekut, Lancaster, Pa., assignor to Radio Corporation of America, a corporation of Delaware Continuation of abandoned application Serial No. 68,173, December 30, 1948.

This application February 25, 1953, Serial No. 338,749

7 Claims.

This invention relates to cooling or heat exchange units or devices through which a coolant is circulated and particularly to such units composed of a plurality of similar iins or blades disposed in thermal or heat transferring relationship with an object to be cooled.

During the continued development of electron discharge devices a serious limitation has been the provision of eicient low cost cooling units. Coolers for electron discharge devices are used to effect the cooling or transfer of heat developed by the operation of the device, which heat, by conduction, is conveyed in common practice to some form of conventional device employing ns or blades which radiate from a core surrounding or concentric with the device. It may be said that the optimum efficiency of such'devices depends to a large extent on their being maintained within a critical temperature range during opleration.

Thus a principal object of my invention is to provide a cooler which is more efficient and low- .erin cost characterized by simplicity of construction and may be made inmass` production of duplicate or single standard iins of a given size for a given cooler type.

Another object is to provide increased cooling effects without reducing the metal surface area available in the original material or blanks from which the fins comprising the cooler assembly are formed.

Another object is the provision of a fin construction in which the punched out portions or louvers present a minimum of cross-sectional area to the air stream, thus reducing the pressure necessary to force the required air ilow through the cooler.

Another object is the provision of a lin construction which not only reinforces the fin per se but also the entire cooler or iin assembly.

Still other objects will appear as the nature of my invention is more fully understood from the Yfollowing description taken in conjunction with the accompanying drawings wherein like parts are designated by identical numerals in the several views.

In the accompanying drawings, wherein, by way of illustration, one form my invention may take is shown:

Figure l is an elevational View of a cooling unit constructed in accordance with my invention and in conjunction with an electron discharge device;

Figure 2 is a top plan view of the unit shown in Figure 1 with the electron discharge device removed;

Figure 3 is a front elevational view on an enlarged scale of one of the ns;

Figure 4 is an end view thereof with an additional fin shown in juxtaposition for convenience;

Figure 5 is a sectional view through the line 5 5 of Figure 3 in the direction. of the arrows;

Figure 6 is a perspective View of a modiiied fin;

Figure '7 is a longitudinal sectional view of a iin having a continuous surface with the formation of stagnant air lm indicated;

Figure 3 is a view similar to Figure 5 with the stagnant air film also indicated; and

Figure 9 is a sectional View of a still further modied iin.

In carrying out my invention I may provide a radiator or cooling unit having a plurality of radially disposed ns each of which is provided with a plurality of offset members or ribs which are punched out but remain integral at both ends with the main bodyportion of the fin; thus Y providing a discontinuous n surface having a plurality of edges and yet which oiers minimum resistance to the flow of the coolant through the radiator.

Referring now to the drawings in detail, Figures l and 2 illustrate one form which my invention may take when utilized in connection with an object such as an electron discharge device indicated generally at I0. The device I0 to be cooled has a radiator II disposed in thermal or heat transferring relation with respect thereto as will be clearly pointed out hereinbelow. As most clearly shown in Figure 2, radiator II includes a core I2 which may enclose all or part of the object to be cooled. Though core I2 is shown as being substantially cylindrical, the core may take any desired form and as will be seen may even be dispensed with entirely. Radially disposed about the periphery oi core I2 are cooling ns or blades I3 each of which may be similar in every respect one to the other.

One such iin I3, shown most clearly in Figures 3, 4 and 5, has a body portion or member I4, a mounting ange I5 along the inner side of the body portion or member and a spacer flange portion I6 along the other.

As stated, the inner edge of body member I4 is provided with a mounting flange i5 which may be integral therewith or connected thereto by any convenient means such as welding or the like. Flange I5 is struck up from body member Ill at a suitable angle with respect thereto and has a shoulder or bend forming an offset portion I5' (Figure 4) permitting the mounting iianges of adjacent ns to nest one with the other as shown.

The body portion I4 of iin I3 has a plurality of heat transfer elements or ribs il' which may be formed by slitting member Iii intermediate its sides into a plurality of strips and then expanding alternate strips to form ribs which lie in a plane outside that of member Ill. If desired, the

ribs may be connected to member Id over suitably' formed openings by means of welding or other means as may be more convenient in the case ,of fins of considerable size. In forming ribs Il end portion i8 is made longer than end portion I9,

thus advantage is taken of the increasing distance between adjacent iins I3 as the radial distance from core I2 increases. By maintaining the surfaces of ribs II between end portions I8 and I9 substantially parallel to body member I4, as is most clearly shown in Figure 5, the only obstruction to the flow of coolant does not exceed the cross section area of the expanded sections or ribs and is thus held to a minimum.

Core I2 and fins I3 may be made from any suitable material such as copper. The cooling unit or radiator Il may be assembled by placing a length of cooper tubing which forms core I2 in a suitable position. Then the ns which may be vdie-formed are brushed with flux and assembled to the core, making a lap-joint with the smooth core surface, and locking or nesting into each adjoining nn. The fins are accurately self spaced by spacer flange I6. When the fins are assembled the cooling unit is heated to brazing temperature and a brazing alloy is applied. I apply the brazing alloy at one end of the cooler at the joint between iins I3 and core I2. When the brazing alloy has emerged at the other end of the cooler, the brazing is completed, at which time the unit is ready to be soldered to the electron discharge device as shown in Figure 1.

As thus assembled the unit is placed in a forced air duct (not shown) in which the coolant air flows in the direction of arrow 20. In operation I have found such a unit or radiator assembly so far more efficient than those heretofore in use that large reductions in cost and weight result. One factor which reduces the cost and weight of the cooling unit is the substantial reduction of material such as copper metal required.

I conducted a comparison test between two coolers of identical size and construction and made from identical materials except that one cooler had fiat fins of continuous surface while the other was provided in accordance with my invention with slit and expanded ribs. Each cooler contained the same number of fins, soldered to a 1% outside diameter copper core. The data obtained is tabulated below.

more than 50%.

Air Flow, Static Presses en Sgm,

er nc es o C- WM Minute Water Continuous Fin Cooler... 160 2, 700 275 l. 81 Slit and Expanded Fin Cooler 160 2, 700 142 8l From the foregoing it is apparent that both cores were supplied with a heat input of 2700 watts. To maintain the continuous iin cooler core at 160 C. it was necessary to force 2T 5 cubic feet of air per minute through the cooler with a static pressure of 1.81 inches of water. In the case of the slit and expanded iin cooler it was necessary to force only 142 cubic feet of air per minute through the same and even though more obstructions are presented to the flow of the coolant only .81 inch of water static pressure was required to attain the rated air flow. As will appear, a slit and expanded fin cooler operated with air now greater than 142 cubic feet per minute may be substantially reduced in size. In some cases the saving of materials has been In View of the fact that material cost represents more than '15% of the cost factor in the production of these units such a saving in materials is highly important.

The foregoing test data was based on the following technique. Due toits-accessibility, the

top of the core is regarded as the point to which temperatures are referred. Air flow was measured by means of a Pitot traverse, as described by Standard Test Code, Bulletin No. 103, National Association of Fan Manufactures. In this method a standard Pitot tube is inserted into a straight section of the duct carrying air to the cooled device. Two traverses (at right angles) are made, each containing eleven velocity pressure readings. rEhe mean square root, (\/P v) avg., is found and velocity calculated from the relation where V is velocity in feet per minute and Pv is Velocity pressure in inches of water. Flow quantity (cfm.) was found by multiplying the velocity by the cross-sectional duct area.

Static pressure was measured by drilling a 1/8 inch diameter hole in the duct at least one duct diameter below the bottom of the cooler to which a lead-off tube was soldered. The lead-ofi tubing was connected to an inclined manometer to determine static pressure.

The improved thermal characteristics of fins constructed in accordance with my invention and coolers made therefrom may be explained as follows. The relation @2h08 (tr)mean (l) is one describing those factors upon which the rate of heat transfer from metal to air is dependent, Where qzrate of heat transfer, B. t. u./hr.

hczthe nlm coefficient of heat transfer, B. t. u./hr. (ft.)2 (F.).

szthe transfer area, (ft.)2 and may be considered the major design Variable. The cost of a cooler is roughly proportional to s, which is reflected into the weight and cost of strip metal such as copper required for fins.

(tr)mean=the temperature diiference between metal and air, F., after correction for thermal geometry.

" The terms q and (tmean are constant and are fixed by the maximum ratings of the device being cooled. In the case of an electron discharge device, these constants are fixed by the maximum tube ratings and q would be the maximum rated plate dissipation, plus a fraction of filament power converted from watts to British thermal units per hour.

While the heat transfer by forced convection between a solid and a fluid depends on the specific properties of the materials in question (thermal conductivity, viscosity, specic heat, etc.)Y it is limited primarily by a laminar iilm of the fluid (air) immediately adjacent to the solid (copper). As is shown in Figure 7 Where for clarity the dimensions are exaggerated the presence of the edge reduces the lm thickness at the leading edge of the n to a negligible amount. I-Iowever, the stagnant nlm builds up until a point close to the trailing edge is reached where its thickness is again reduced to a negligible amount. As is lapparent from Figure 8, the build up of stagnant air lm thickness is minimized by increasing the number of edges through the use of ribs. The film coeicient is thus more than doubled in constructions made in accordance with my invention and this makes possible substantial savings as is apparent from Equation "1 above.

When it is desired to dispose the device to be cooled with its axis perpendicular to the coolant stream, `I may construct my ns las, shownin Figure -6 where fin 2| is disc-like having a central opening through Iwhich the electron discharge device may 'exten-d. Such iins are similarly formed with slit and expanded ribs 22 each rso disposed as to prevent leading edges 22 normal to the coolant stream. A plurality of such fins are spaced axially along the anode of the electron discharge device and may be soldered or "brazed directly thereto.

I may also offset -or stagger the 'ribs along such a 1in as fln I3 as indicated in Figure -9 which figure is one similar to Figure 5. Fin 23 is constructed with ribs 24 in the same manner as n- 13 except that adjacent ribs are punched yout unequal distances from the plane of the iin. In'v such case, I may stagger the ribs in groups of three, every third iin being in the same plane. 'Io permit proper spacing of the fins about the core adjacent fins have ribs which have been similarly staggered.

Instead of assembling fins I3 to core l2 with all the edges thereof in alinement, I may displace alternate fins axially to stagger the ribs of adjacent ns.

From the foregoing, it is apparent that my invention provides fins and cooling units of greatly enhanced eiciency and which may be mass produced at a substantially lower cost and utilizing considerably less material than heretofore. 4Though I have described my invention in connection `with forced air coolers for use with electron vdischarge devices, it is to be understood that my invention is equally applicable to other lair vcooled devices and also tothe cooling of Adevices utilizing a liquid coolant. Thus, while I have set forth the foregoing embodiments of my invention and described it in detail with respect thereto, I do not wish to be limited to the exact construction set forth but desire to claim all modifications thereof that come within the scope of the appended claims.

vI claim:

1. A cooling unit for an electron discharge device -having an external anode, the unit comprising: a means for attaching the unit to the outside surface of said anode: an array of similar planar lhns each attached along one ofits edges to said means and extending therefrom in va plane which is parallel to the axis of the anode,

each of said planar fins having a projecting ange on the inside and outside portion thereof which form an inner and outer tubular wall, said planar fins being spaced at an increasing distance one from another in a radial direction, the spacings between different pairs of adjacent ns being substantially equal; each of said ns having a plurality of successively positioned elongated slots each of a small width as measured in the direc- .tion of said axis as compared to the length of said slot and each extending with its long axis perpendicular to the axis of the said anode; a planar rib extending over each of said slots and lying on one side thereof in a plane which is intermediate that of the fin having said slot and the plane of the iin next adjacent to it on said side, said intermediate plane being parallel to said axis of .the anode and inclined in relation to the plane of its supporting fin, the spacing between the fm and the intermediate plane increasing in a radial direction from said anode; each rib of each iin being connected thereto only at the ends of its corresponding slot, whereby a :duid coolant lwhich is Aprojected at an end of lsaid cooling unit Yin the direction of the axis of said anode to flow between vsaid fins will not be 6 retarded by the friction of continuous surfaces unbroken for the full width thereof.

2. A cooling unit for an Velectron discharge device `having an external cylindrical anode, the unit comprising: a centrally disposed means for attaching the unit `co-axially to the Vcylindrical outside surface of lsaid anode; an annular array of similar Yplanar ns each attached along one of 'its edges to said means and extending radially therefrom in a plane which is parallel to the axis -of the anode, each of said planar ns having a projecting iiange -on the inside and outside portion thereof which form an inner and outer tubular `wal-l, said planar iins being spaced at an increasing distance one from another in a radial direction, the spacings between ldifferent `pairs -of adjacent fins being substantially equal; each of vsaid fins having a plurality of successively positioned elongated slots each of a small width as Ymeasured in the -direction of said axis as compared to the length of the slot and each extending with its long axis perpendicular to the axis of the said anode; 4a planar rib extending over each 'of 'said slots and lying on one side thereof in a plane which is intermediate that of the vfin having said slot and the plane of the fin next adjacent to it on said side, said intermediate plane vbeing parallel to `said axis of the anode land inclined with relation to the plane of its supporting n, the spacing between the plane of Athe iin and the intermedia-te plane increasing in a radial-direction from said anode; each rib of each nn being connected thereto only at the ends of its corresponding slot, whereby a fluid coolant which is projected at an end of said cooling unit in the direction of the axis of said anode to flow between said iins will not be retarded by the friction of continuous surfaces unbroken lfor `the full width thereof.

3. A cooling unit for an electron discharge -device ha-ving an external cylindrical anode, the unit comprising: a centrally disposed means for attaching the unit co-axially to the cylindrical outside surface of said anode; an annular array of similar planar ns each attached along one of its edges to said means and extending radially therefrom in a plane which is parallel to the axis of the anode, each of said planar fins having a projecting flange on the inside and outside portion thereof which form an inner and outer tubular wall, saidplanar fins being spaced at an increasing `distance one from another in a radial direction, thespacings between different pairs of adjacent iins being substantially equal and being progressively wider at progressively greater distances outward from said means; each of said hns having a plurality of successively positioned elongated radially extending slots each of a small width as measured in the direction of said axis as compared to the length of the slot and each extending vwith its long axis perpendicular to the axis of the said anode; a planar rib of the same Width `as-and extending over each of said slots and lying on one side thereof in a plane which is radially intermediate that of the n having said slot and the plane of the iin next adjacent to it on said side, said radially intermediate plane being parallel to said axis of the anode; each rib of each n being connected thereto only at the ends of its corresponding slot, and being progressively further spaced therefrom at progressively greater distances from said means, whereby a -uid coolant which is projected at an end of said cooling unit in the direction of the axis of said anode to flow between said ins will not vbe retarded by the friction of continuous surfaces unbroken for the full width thereof.

4. A cooling unit for an electron discharge device having an external anode, the unit comprising: an array of similar planar ns each attached along one of its edges to said anode and extending therefrom in a plane which is parallel to the axis of the anode, means forming an outer tubular wall which engirdles said array, said planar fins being spaced at an increasing distance one from another in a radial direction, the spacings between diierent pairs of adjacent nns being substantially equal; each of said ns having a plurality of successively positioned elongated slots each of a small width as measured in the direction of said axis as compared to the length oi said slot and each extending with its long axis perpendicular to the axis of the said anode; a planar rib extending over each of said slots and lying on one side thereof in a plane which is intermediate that of the iin having said slot and the plane of the iin next adjacent to it on said side, said intermediate plane being parallel to said axis of the anode and inclined in relation to the plan of its supporting fin, the spacing between the plane of the fin and the intermediate plane increasing in a radial direction from said anode; each rib of each iin being connected thereto only at the ends of its corresponding slot, whereby a uid coolant which is projected at an end of said cooling unit in the direction of the axis of said anode to iiow between said ns will not be retarded by the friction of continuous surfaces unbroken for the full width thereof.

5. A cooling unit for an electron discharge device having an external anode, the unit cornprising: an array of similar planar fins each attached along one of its edges to said anode and extending therefrom in a plane which is parallel to the axis of the anode, means forming an outer tubular wall which engirdles said array, said planar fins being spaced at an increasing distance one from another in a radial direction, the spacings between different pairs of adjacent iins -being substantially equal; each of said ns having a plurality of successively positioned elongated slots each ci a small width as measured in the direction of said axis as comparedk to the length of said slot and each extending with its long axis perpendicular to the axis of the said anode; a planar rib extending over each of said slots and lying on one side thereof in a plane which is intermediate that of the nn having said slot and the plane of the fin next adjacent to it on said side, the ribs lying between adjacent fins all lying substantially in said intermediate plane, said intermediate plane being parallelto said axis of the anode and inclined in relation to the plane of its supporting iin, the spacing vbetween the plane of the fin and the intermediate plane increasing in a radial direction from said anode; each rib of each n being connected thereto only at the ends of its corresponding slot, whereby a fluid coolant which is projected at an end of said cooling unit in the direction of the axis of said anode to flow between said fins will not be retarded by the friction of continuous surfaces unbroken for the full width thereof.

6. A cooling unit for an electron discharge device having an external cylindrical anode, the unit comprising: a centrally disposed means for attaching the unit co-axially to the cylindrical outside surface of said anode; an annular array of similar planar ns each attached along one of its edges to said means and extending radially therefrom in a plane which is parallel to the axis of the anode, said planar ins being spaced at an increasing distance one from another in a radial direction, the spacings between diiierent pairs of adjacent fins being sub-1. stantially equal; each of said fins having a plurality of successively positioned elongated slots each of a small width as measured in the direction of said axis as compared to the length of the slot and each extending with its long axis perpendicular to the axis of the said anode; a planar rib extending over each of said slots and lying on one side thereof in a plane which is intermediate that of the nn having said slot and the plane of the fin next adjacent to it on said side, said intermediate plane being parallel to said axis cf the anode and inclined with relation to the plane of its supporting iin, the spacing between the plane of the iin and the intermediate plane increasing in a radial direction from said anode; each rib of each iin being connected thereto only at the ends of its corresponding slot, whereby a uid coolant which is projected at an end of said cooling unit in the direction of the axis of said anode to now between said fins will not be retarded by the friction of continuous surfaces unbroken for the full width thereof.

7. A cooling unit for an electron discharge device having an external cylindrical anode, the unit comprising: a centrally disposed means for attaching the unit co-axially to the cylindrical outside surface oi said anode; an annular array of similar planar iins each attached along one of its edges to said means and extending radially therefrom in a plane which is parallel to the axis of the anode, each of said planar fins having a projecting ange on the outside portion thereof which forms an outer tubular wall, said planar nns being spaced at an increasing distance one from another in a radial direction, the spacings between diierent pairs of adjacent fins being substantially equal and being progressively Wider at progressively greater distances outward from said means; each of said fins having a plurality of successively positioned elongated radially extending slots each of a small width as measured in the direction of said axis as compared to the length of the slot and each extending with its long axis perpendicular to the axis of the said anode; a planar rib of the same width as and extending over each of said slots and lying on one side thereof in a plane which is radially intermediate that of the iin having said slot and the plane of the fin next adjacent to Ait on said side, said radially intermediate plane being parallel to said axis of the anode; each rib of each fin being connected thereto only at the ends of its corresponding slot, and being progressively further spaced therefrom at progressively greater distances from said mea-ns, whereby a fluid coolant which is projected at an end of said cooling unit in the direction of the axis of said anode to flow between said ns will not be retarded by the friction of continuous surfaces unbroken for the full width thereof.

References Cited in the file 0i' this patent UNITED STATES PATENTS Number Name Date 2,419,234 Holihan Apr. 22, 1947 2,512,143 Dailey June 20, 1950 2,535,721 Chausson Dec. 26, 1950 2,558,752 Holm July 3, i951 2,606,007 Simpelaar Aug. 5, 1952 

